In fast high-quality elevators, good travelling comfort is an objective of increasing importance. Lateral swing, i.e. horizontal vibration of the passenger cabin of the elevator, is the predominant parameter of travelling comfort, and its quality is a significant factor in discussions relating to the travelling comfort provided by an elevator.
Lateral swing may arise from several causes, but the primary causes are short, comparatively sharp bends and deflections in the guide rail line. The task of straightening these bends is generally the more difficult the longer the line is. On the other hand, long guide rail lines are generally used with faster elevators, and increased speed again means that the effect of bends and deflections in producing lateral swing becomes more pronounced.
The need to minimize lateral swing is greatest in the case of top-quality elevators, tall buildings and especially elevators serving the top floors of the building. These elevators travel through long distances along the guide rails at a high speed. Therefore, to achieve the required low level of lateral swing, the guide rail line must be very straight.
The equipment currently used for checking the straightness of the alignment of elevator guide rails, controlling the quality of guide rail lines, and charting the lines and the lateral deflections in them, requires special instrumentation and is quite bulky and complex. In addition, rendering the results obtained into a form usable for the straightening of deflections requires subsequent calculations by means of computers. Such a solution, which is technically very demanding, may be acceptable in research and product development, but it is not very practical or efficient when new guide rail lines are to be installed or old ones improved.
The means used at the site of installation, to check the straightness of the line, are often of a rather coarse nature, for example using a ruler or plumb line. Even visual estimates of the line quality have been resorted to. Thus, the estimates of line quality made in connection with actual installations have been ambiguous and have been dependent on the experience and skill of the estimator. As the repeatability of the measurement is low, it is generally not possible to obtain sufficiently reliable estimates of the quality of the corrections made.
Since the quality and straightness of the alignment of elevator guide rail lines may vary considerably from rail to rail and in different parts of the shaft, there is a requirement for means able to inspect complete installed guide rail lines easily and reliably. Similarly, there is a requirement to control the quality of corrections to guide rail lines as accurately as possible even during the execution of the corrections.